Diclofenac　sodium,　as　a　typical　deputation　of　non-steroidal　anti-inflammatory　drugs,　is　widely　used　in　clinical　treatment.　Due　to　the　heavy　use,　diclofenac　sodium　is　commonly　detected　in　water　environment,　and　the　removal　of　diclofenac　sodium　from　wastewater　is　important　for　environmental　protection.　Notably,　magnetic　separation　technology　has　become　a　novel　performance　in　the　removal　of　organic　pollutants　from　wastewater　in　recent　years.　Herein,　we　engineered　a　lignin-based　magnetic　nanoparticle　adsorbent　(LMNA)　by　loading　a　magnetic　core　(Fe3O4)　onto　alkali　lignin.　This　novel　adsorbent　has　the　advantage　of　green　synthesis　and　low　cost,　making　it　an　ideal　material　for　wastewater　treatment.　Remarkably,　the　BET　surface　area　of　LMNA　(739.2　m2 g−1)　was　higher　than　that　of　alkali　lignin　(2.2　m2 g−1).　Adsorption　batch　experiments　confirmed　that　the　LMNA　exhibited　good　adsorption　performance　to　diclofenac　sodium　with　a　higher　adsorption　capacity　of　106.4 mg g−1.　The　adsorption　kinetic　data　and　isothermal　were　well　fitted　by　the　pseudo-second-order　rate　equation　(R2　=　0.980)　and　the　Langmuir　equation　(R2　=　0.991),　respectively.　Moreover,　the　reaction　mechanisms　between　the　diclofenac　sodium　and　LMNA　mainly　related　to　the　synergism　of　electrostatic　attractions,　π–π　stacking　interactions　and　hydrogen　bonding　interactions.　Especially,　the　LMNA　exhibited　high　magnetic　saturation　strength　(10.5　emu　g−1)　which　made　it　easy　to　recycle,　showing　excellent　reusability　(4　cycles).　Our　work　might　introduce　significant　theoretical　and　experimental　basis　for　realizing　excellent　adsorption　of　emerging　organic　pollutants　from　wastewater　by　the　magnetic　nanoparticle　adsorbent.　Graphic　Abstract:　[Figure　not　available:　see　fulltext.].　©　2021,　The　Author(s),　under　exclusive　licence　to　Springer　Science+Business　Media,　LLC,　part　of　Springer　Nature.